Duplex pipe end working method

ABSTRACT

A duplex pipe ( 10 ) is cut with a cutting tool ( 30 ), for cutting connecting ribs ( 13 ) from the end face of the duplex pipe ( 10 ) which is held with an outer pipe ( 11 ) chucked (rib cutting step). The duplex pipe ( 10 ) is cut from the end face of the duplex pipe ( 10 ) up to the portion thereof corresponding to the exposed length of the inner pipe ( 12 ) to thereby form a slit ( 21 ) in the outer pipe ( 11 ) and connecting ribs ( 13 ) (slit forming step). The cutting tool ( 30 ) has a guide hole ( 31 ) into which the inner pipe ( 12 ) can be inserted while guiding the inner pipe outer peripheral surface ( 12   a ), a cutting device ( 32 ) for cutting the connecting ribs ( 13 ), and a guide pin ( 33 ) which can be inserted into the inner pipe ( 12 ) while guiding the inner pipe inner peripheral surface ( 12   b ).

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 09/816,345 filed Mar. 26,2001, now U.S. Pat. No. 6,658,717 the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates a duplex pipe end working method and aduplex pipe end working apparatus in which an end portion of a duplexpipe comprising an outer pipe, an inner pipe and connecting ribs moldedinto an integral body by extrusion working or by drawing working isskinned, more specifically, the outer pipe and connecting ribs of theduplex pipe are respectively cut in such a manner that the inner pipecan be projected outwardly of the outer pipe and can be thereby exposedto the outside.

2. Description of the Related Art

As conventionally known, a duplex pipe comprises an outer pipe throughwhich a first fluid flows and an inner pipe disposed inside the outerpipe, through which a second fluid flows. According to the manufacturingmethod thereof, the duplex pipe can be roughly classified into twotypes. That is, one of them is a duplex pipe of a type that an outerpipe and an inner pipe are manufactured individually, and the outer pipeis drawing worked with the inner pipe inserted into the outer pipe,whereby projections provided on the inner wall of the outer pipe arepressure contacted with the outer wall of the inner pipe; and, the otheris a duplex pipe of a type that an outer pipe, an inner pipe andconnecting ribs for connecting together the inner and outer pipes aremolded into an integral body by extrusion working or by drawing working.In recent years, from the viewpoint of reduction in the manufacturingcost thereof, there has been widely used the duplex pipe of the lattertype that the outer pipe, inner pipe and connecting ribs are molded intoan integral body.

In the case of the duplex pipe, a joint of a flange type or a nut-uniontype is connected to the end portion thereof before it is actually used.Thus, in the case of the duplex pipe of the latter type, for connectionof such joint, a duplex pipe end working operation is performed on theend portion of the duplex pipe, that is, the end portions of the outerpipe and connecting ribs are respectively cut in such a manner that theinner pipe can be projected outwardly of the outer pipe.

Now, FIGS. 10A to 10C are respectively views of a conventional duplexpipe, showing how the end portion of the duplex pipe is worked. As shownin FIG. 10A, a duplex pipe 10, which is held by chucking an outer pipe11, is rotated and, while moving a cutting tool 55 in the axialdirection of the duplex pipe 10 (in FIG. 10A, in the direction of anoutline arrow mark) from the end face of the duplex pipe 10, the outerpipe 11 and connecting ribs 13 are cut. In case where the cutting tool55 is moved up to a position corresponding to the exposed length of theinner pipe 12, as shown in FIG. 10B, the outer pipe 11 and connectingribs 13 are cut so that the inner pipe 12 can be projected outwardly ofthe outer pipe 11 and can be thereby exposed to the outside.

By the way, in the case of the duplex pipe 10 in which the outer pipe11, inner pipe 12 and connecting ribs 13 are molded into an integralbody, due to its manufacturing method using extrusion working or drawingworking, it is difficult that the center line of the outer pipe 11 ismade to coincide with the center line of the inner pipe 12.

As in the above-mentioned conventional duplex pipe end working method,in case where, while chucking the outer pipe 11 and rotating the duplexpipe 10, the outer pipe 11 and connecting ribs 13 are cut according toan ordinary pipe working method using the cutting tool 55, as shown inFIG. 10C, there are produced an excessively worked portion a and anunworked portion b and, therefore, it is difficult to work the innerpipe 12 in such a manner that the thickness thereof can be made uniformover the whole periphery thereof. The reason for this is that, in casewhere the duplex pipe 10 is worked with the outer pipe 11 chucked, theouter and inner pipes 11 and 12 are not positioned on the sameconcentric axis; and, therefore, even in case where the cutting tool 55is moved with the outer pipe 11 as a reference, the positional relationof the inner pipe 12 and cutting tool 55 cannot be made constant. Also,since an amount or a direction in which the center line of the innerpipe 12 is displaced from the center line of the outer pipe 11 is notconstant, it is impossible to bring the inner pipe 12 to an on-centerposition while chucking the outer pipe 11.

In case where the thickness of the exposed inner pipe 12 is not uniform,when the inner pipe 12 is punched or rolled, a crack occurs in the innerpipe 12. For this reason, according to the conventional working method,in fact, it is impossible to execute a punching operation on the exposedinner pipe end portion after the duplex pipe end portion is worked.

Further, as enlargedly shown in FIG. 10C, burrs 56 occur in the endportions of the connecting ribs 13. While the burrs 56 remain unremoved,the flow resistance of the fluid flowing through the outer pipe 11 isincreased and thus the flowing noise of the fluid when it flows throughthe outer pipe 11 is also increased. Therefore, after completion of thecutting operation by the cutting tool 55, it is necessary to execute apost-treatment operation for removing the burrs 56. Also, because thereare present many portions from which the burrs 56 must be removed, it isdifficult to control the cleaning of the cut powders. In case where thecleaning of the cut powders is insufficient, the connecting ribs 13 canbe contaminated, which results in the poor sealing.

Moreover, since the outer pipe 11 and connecting ribs 13 arerespectively cut away in their end portions by the amounts thatcorrespond to the exposed portion of the inner pipe 12, the cuttingmargins of the outer pipe 11 and connecting ribs 13 are large, whichgives rise to production of a large amount of cut powders. Due to this,the above-mentioned cleaning control of the cut powders is made moretroublesome and difficult.

SUMMARY OF THE INVENTION

An object of the invention is to eliminate the above-mentioned drawbacksfound in the conventional duplex pipe end portion working method.Accordingly, it is also an object of the invention to provide a duplexpipe end working method and a duplex pipe end working apparatus whichcan be applied to an operation to skin or cut the end portion of aduplex pipe comprising an outer pipe, an inner pipe and connecting ribsmolded together as an integral body by extrusion working or by drawingworking, can make uniform the thickness of the inner pipe, can preventburrs from occurring in the end portions of the connecting ribs, and canreduce the quantities of cut powders produced.

In attaining the above object, according to the invention, there areprovided the following duplex pipe end working method and apparatus.

(1) According to a first aspect of the invention, there is provided aduplex pipe end working method for working the end portion of a duplexpipe comprising an outer pipe, an inner pipe disposed inside the outerpipe, and connecting ribs respectively for connecting together the outerand inner pipes formed into an integral body by extrusion working or bydrawing working to skin or cut the outer pipe and connecting ribs insuch a manner that the inner pipe can be projected outwardly of theouter pipe and can be thereby exposed to the outside, the duplex pipeend working method comprising: a rib cutting step of cutting theconnecting ribs along the axial direction of the duplex pipe at and fromthe end face of the duplex pipe, using a cutting tool including a guidehole which, while guiding the outer peripheral surface of the inner pipethat is held by chucking the outer pipe, allows the inner pipe to beinserted thereinto, and a cutting device for cutting the connectingribs; and, a slit forming step of cutting the duplex pipe at and fromthe end face of the duplex pipe up to the portion thereof correspondingto the exposed length of the inner pipe to thereby form a slit in theouter pipe and connecting ribs.

(2) According to a second aspect of the invention, there is provided aduplex pipe end working method for working the end portion of a duplexpipe comprising an outer pipe, an inner pipe disposed inside the outerpipe, and connecting ribs respectively for connecting together the outerand inner pipes formed into an integral body by extrusion working or bydrawing working to skin or cut the outer pipe and connecting ribs insuch a manner that the inner pipe can be projected outwardly of theouter pipe and can be thereby exposed to the outside, the duplex pipeend working method comprising: a slit forming step of cutting the duplexpipe at and from the end face of the duplex pipe up to the portionthereof corresponding to the exposed length of the inner pipe to therebyform a slit in the outer pipe and connecting ribs; and, a rib cuttingstep of cutting the connecting ribs along the axial direction of theduplex pipe at and from the end face of the duplex pipe, using a cuttingtool including a guide hole which, while guiding the outer peripheralsurface of the inner pipe that is held by chucking the outer pipe,allows the inner pipe to be inserted thereinto, and a cutting device forcutting the connecting ribs.

(3) According to a third aspect of the invention, in a duplex pipe endworking method as set forth in the first (1) or second (2) aspect, whilerotating the cutting tool, the cutting tool is moved in the axialdirection of the duplex pipe to thereby cut the connecting ribs.

(4) According to a fourth aspect of the invention, in a duplex pipe endworking method as set forth in the first (1) or second (2) aspect, thecutting tool is pressed in the axial direction of the duplex pipe tothereby cut the connecting ribs.

(5) According to a fifth aspect of the invention, in a duplex pipe endworking method as set forth in any one of the first (1) to fourth (4)aspects, the cutting tool is structured such that a guide pin, which,while guiding the inner peripheral surface of the inner pipe, allows theinner pipe to be inserted thereinto, is disposed in the guide hole.

(6) According to a sixth aspect of the invention, there is provided aduplex pipe end working apparatus for working the end portion of aduplex pipe comprising an outer pipe, an inner pipe disposed inside theouter pipe, and connecting ribs respectively for connecting together theouter and inner pipes formed into an integral body by extrusion workingor by drawing working to skin or cut the outer pipe and connecting ribsin such a manner that the inner pipe can be projected outwardly of theouter pipe and can be thereby exposed to the outside, the duplex pipeend working apparatus comprising: a cutting tool including a guide holewhich, while guiding the outer peripheral surface of the inner pipe thatis held by chucking the outer pipe, allows the inner pipe to be insertedthereinto, and a cutting device for cutting the connecting ribs, thecutting tool being capable of cutting the connecting ribs along theaxial direction of the duplex pipe at and from the end face of theduplex pipe.

(7) According to a seventh aspect of the invention, in a duplex pipe endworking apparatus as set forth in the sixth aspect (6) of the invention,the cutting tool can be rotated and can be moved along the axialdirection of the duplex pipe.

(8) According to an eighth aspect of the invention, in a duplex pipe endworking apparatus as set forth in the sixth aspect (6) of the invention,the cutting tool can be pressed along the axial direction of the duplexpipe.

(9) According to a ninth aspect of the invention, in a duplex pipe endworking apparatus as set forth in the sixth aspect (6) of the invention,the cutting tool is structured such that the cutting device can bereplaced.

(10) According to a tenth aspect of the invention, in a duplex pipe endworking apparatus as set forth in any one of the sixth (6) to ninth (9)aspects of the invention, the cutting tool is structured such that aguide pin which, while guiding the inner peripheral surface of the innerpipe, allows the inner pipe to be inserted thereinto is disposed in theguide hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the end portion of a duplex pipe.

FIGS. 2A to 2D are respectively conceptual views of a duplex pipe endworking method according to a first embodiment of the invention and aworking procedure to be executed by a duplex pipe end working apparatuswhich can enforce the present duplex pipe end working method.

FIGS. 3A and 3B are respectively perspective and sectional views of themain portions of a cutting tool used in the first embodiment.

FIG. 4 is an enlarged conceptual view of a cutting operation to beexecuted by the above cutting tool, showing how the duplex pipe endportion is cut using the cutting tool.

FIGS. 5A to 5D are respectively conceptual views of a duplex pipe endworking method according to a second embodiment of the invention as wellas a working procedure to be executed by a duplex pipe end workingapparatus which can enforce the present duplex pipe end working method.

FIGS. 6A and 6B respectively show the concept of a third embodimentaccording to the invention; that is, they are conceptual views of aworking procedure for cutting connecting ribs 13 according to the thirdembodiment of the invention;

FIG. 7 is a perspective view of a cutting tool employed in a fourthembodiment of the invention.

FIGS. 8A and 8B respectively show the concept of a fifth embodimentaccording to the invention; that is, they are conceptual views of aworking procedure for forming a slit according to the fifth embodimentof the invention.

FIG. 9 is a section view of a joint for connecting together two duplexpipes the end portions of which have been worked according to theinvention.

FIGS. 10A and 10C are respectively views of a conventional duplex pipeend working method.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described below with reference tothe accompanying drawings.

First Embodiment

FIG. 1 is a perspective view of the end portion of a duplex pipe; FIGS.2A to 2D are respectively conceptual views of a duplex pipe end workingmethod according to a first embodiment of the invention and a workingprocedure to be executed by a duplex pipe end working apparatus whichcan enforce the present duplex pipe end working method; FIGS. 3A and 3Bare respectively perspective and sectional views of the main portions ofa cutting tool used in the present embodiment; and, FIG. 4 is anenlarged conceptual view of a cutting operation to be executed by thecutting tool, showing how the duplex pipe end portion is cut using thecutting tool.

As shown in FIG. 1, a duplex pipe 10 to be used as a work is formed insuch a manner that an outer pipe 11, an inner pipe 12 and connectingribs 13 for connecting together the outer and inner pipes 11 and 12 aremolded of aluminum material by extrusion working or by drawing workinginto an integrated body. In case where the duplex pipe 10 is used arefrigerant pipe in the cooling cycle of an air conditioner for a car,the outside diameter of the outer pipe 11 is of the order of □ 16-25 mmand the outside diameter of the inner pipe 12 is of the order of □ 6-12mm. The connecting ribs 13 are disposed in such a manner that theydivide a space, which is formed between the outer and inner pipes 11 and12, into three sections. Since three connecting ribs 13 are disposed,they can balance well respect to three-axis bending, which can increasethe freedom of a bending design. Also, the three connecting ribs 13 canprovide good balance when the duplex pipe 10 is worked by extrusion.

Now, description will be given below of the procedure for working theend portion 10 a of the duplex pipe 10, that is, skinning or cutting theouter pipe 11 and connecting ribs 13 in such a manner that the innerpipe 12 can be projected outwardly of the outer pipe 11 and can bethereby exposed to the outside, with reference to FIGS. 2A to 2D.

Firstly, as shown in FIG. 2A, the outer pipe 11 is chucked by a clamp 20to thereby hold the duplex pipe 10 and, as shown in FIGS. 2A and 2B, theconnecting ribs 13 are respectively cut along the axial direction of theduplex pipe 10 from the end face of the duplex pipe 10, that is, a ribcutting operation is executed (a rib cutting step). From the view pointof reducing the cutting margins of the connecting ribs 13, preferably,the rib cutting operation may be executed only on the base end portionsof the connecting ribs 13, that is, only on the portions of theconnecting ribs 13 that are connected to the outer peripheral surface 12a of the inner pipe 12.

In the rib cutting operation, there is used a cutting tool 30. And, thecutting tool 30 comprises a guide hole 31 into which the inner pipe 12can be inserted while guiding the outer peripheral surface 12 a of theinner pipe 12, and a cutting device 32 which is used to cut theconnecting ribs 13. Also, the cutting tool 30 further includes a guidepin 33 which is disposed within the guide hole 31 and can be insertedinto the inner pipe 12 while guiding the inner peripheral surface 12 bof the inner pipe 12. The inside diameter of the guide hole 31 is almostequal to or slightly smaller than the outside diameter of the inner pipe12, while the outside diameter of the guide pin 33 is almost equal to orslightly smaller than the inside diameter of the inner pipe 12.

The cutting tool 30 is disposed in such a manner that it can be rotatedas well as can be moved in the axial direction of the duplex pipe 10. Inoperation, while rotating the duplex pipe 10 and cutting tool 30, thecutting tool 30 is moved in the axial direction of the duplex pipe 10 tothereby cut the connecting ribs 13. The cutting operation of theconnecting ribs 13 is carried out until the leading end of the cuttingdevice 32 reaches the positions of the connecting ribs 13 thatcorrespond to the exposed length of the inner pipe 12. In case wherecutting of the connecting ribs 13 by a given dimension is completed, thecutting tool 30 is pulled out from the duplex pipe 10. On the right side(in FIGS. 2A to 2D) of the position where the leading end of the cuttingdevice 32 has reached, there is formed a clearance 13 a (see FIG. 2C)between the outer peripheral surface 12 a of the inner pipe 12 and thecut surfaces of the connecting ribs 13. By the way, in the rib cuttingoperation, the duplex pipe 10 may not be rotated.

Next, as shown in FIG. 2C, the portion of the duplex pipe 10 whichextends from the end face of the duplex pipe 10 to the position wherethe leading end of the cutting device 32 of the cutting tool 30 hasreached, that is, the portion of the duplex pipe 10 which corresponds tothe exposed length of the inner pipe 12 is cut or slitted to therebyform a slit 21 in the outer pipe 11 and connecting ribs 13 (slit formingstep).

In the slit forming operation, there is used a metal saw 22. Inoperation, while rotating the duplex pipe 10 and metal saw 22, the metalsaw 22 is moved in the direction of an arrow mark shown in FIG. 2C tothereby form the slit 21. The width of the slit 21 is of the order of 1mm. The slit 21 is formed such that it reaches the clearance 13 a.

Due to formation of the slit 21, on the leading end side (in FIG. 2C, onthe right side) of the duplex pipe 10 that is located forwardly of theslit 21, the connection between the outer and inner pipes 11 and 12 iscut. Therefore, as shown in FIG. 2D, in case where the leading end sideportion of the duplex pipe 10 located forwardly of the slit 21 is pulledout, the inner pipe 12 is projected outwardly of the outer pipe 11 andis thereby exposed to the outside. This completes the duplex pipe endworking operation.

Referring now to FIGS. 3A and 3B, the cutting tool 30 comprises acylindrical-shaped holder 36 in which the guide hole 31 is formed. Theholder 36 is structured such that the leading end thereof has asubstantially frustum-shaped section and a portion of the holder 36 inthe peripheral direction thereof is cut away to thereby form an opening34 communicating with the guide hole 31. The cutting device 32, which isused to cut the connecting ribs 13, is disposed in one inside edge ofthe opening 34. Also, the leading end portion of the guide pin 33 isformed in a hemi-spherical shape and is projected outwardly of theleading end of the cutting device 32. The guide pin 33 is disposed suchthat it is connected to the holder 36 while the axis thereof iscoincident with the axis of the holder 36. Also, the guide pin 33 can berotated together with the holder 36. The axes of the guide pin 33 andholder 36 provide the axis of the cutting tool 30.

In operation, the cutting tool 30 is moved forward toward the duplexpipe 10 with the axis thereof coincident with the axis of the outer pipe11. The end portion 10 a of the duplex pipe 10 is projected outwardly ofthe portion of the duplex pipe 10 that is chucked by the clamp 20 and,therefore, the end portion 10 a is flexible to a certain degree. Thus,even in case where the center of the inner pipe 12 is slightly displacedfrom the center of the outer pipe 11, the guide pin 33 can be insertedinto the inner pipe 12 smoothly. As the guide pin 33 is inserted, theaxis of the inner pipe 12 is allowed to coincide with the axis of thecutting tool 30, thereby being able to correct the above-mentioneddisplacement of the inner pipe 12. Also, insertion of the guide pin 33can prevent the axis of the cutting tool 30 from swinging oroscillating.

In case where the cutting tool 30 is moved further forward after theguide pin 33 is inserted into the inner pipe 12, the inner pipe 12 isinserted into the guide hole 31, while the outer peripheral surface 12 athereof being guided by the inner peripheral surface of the of the guidehole 31. Such insertion of the inner pipe 12 into the guide hole 31 canalso correct the above-mentioned displacement of the inner pipe 12.

As shown in FIG. 3B, the leading end portion 32 a and trailing endportion 32 c of the cutting device 32 are respectively so formed as tohave an R-shaped section: and, the diameter of the main body portion 32b of the cutting device 32 is set as □ b, whereas the diameter of theleading end portion 32 a is set as □ a (□ a>□ b). The reason for this isthat, as shown in FIG. 4, after the connecting ribs 13 are cut using thecutting device leading end portion 32 a, the inner pipe 12 is swaged tothereby enhance the surface precision of the inner pipe outer peripheralsurface 12 a. The clearance dimension between the cutting device mainbody portion 32 b and guide pin 33 is set as a dimension which issuitable for swaging of the inner pipe 12. Such setting of the clearancedimension can decide the thickness of the inner pipe 12 after theconnecting ribs 13 are cut, so that, while the inner pipe 12 is beingswaged, the thickness thereof can be made uniform over the entireperiphery thereof.

Further, as shown in FIG. 3B, on the trailing end side of the cuttingdevice 32, there is formed a so called relief 35, while the diameter ofthe relief 35 is set as □ c (□ c>□ b). The reason for this is to reducethe working resistance of the cutting device 32 to thereby extend thelife of the cutting device 32.

According to the first embodiment, due to formation of the slit, burrsare hard to occur in the end portions of the connecting ribs 13. Therestricted occurrence of the burrs can prevent an increase in the flowresistance of the first fluid flowing through the outer pipe 11, therebybeing able to prevent the flowing noise of the first fluid when it flowsthrough the outer pipe 11 from being louder. Also, there is eliminated apost-treatment operation for removing burrs, which makes it possible tosimplify the duplex pipe end working operation. Even if a post-treatmentoperation was necessary, burrs occurring in the embodiment are forsmaller in number than in the prior art and, therefore, thepost-treatment operation is much easier. This can facilitate thecleaning control of the cut powders involved with the burr removingoperation and thus can prevent poor sealing due to contamination.

Also, according to the embodiment, after the guide pin 33 of the cuttingtool 30 is inserted into the inner pipe 12 and the displacement of theinner pipe 12 is corrected such that the axis thereof can be matched tothe axis of the cutting tool 30, the connecting ribs 13 are cutrespectively. Therefore, while keeping the thickness of the innersurface 12 uniform over the entire periphery thereof, the connectingribs 13 can be cut respectively in the axial direction of the duplexpipe 10. Also, since the inner pipe 12 can be held in a centered stateby the guide pin 33 inserted therein, not only when the connecting ribs13 are cut, but also when the outer peripheral surface 12 a of the innerpipe 12 is cut in part, the thickness of the inner pipe 12 can be keptuniform over the entire periphery thereof.

Further, when the duplex pipe 10 is manufactured by extrusion working,the hole formed on the inner peripheral surface 12 b side of the innerpipe 12 provides sufficiently high roundness due to the characteristicof the manufacturing method thereof. Thus, by inserting the guide pin 33into the high-roundness hole of the inner pipe 12 to thereby guide theinner pipe inner peripheral surface 12 b, the precision with which thedisplacement of the inner pipe 12 is corrected can be enhanced. In thisrespect as well, the thickness of the inner pipe 12 can be made furtheruniform.

Since the thickness of the inner pipe 12 can be restricted according tothe clearance dimension between the cutting device main body portion 32b and guide pin 33, use of the guide pin 33 is especially effective whenthe inner pipe 12 is swaged and when the inner pipe 12 varies inthickness at the stage when the duplex pipe 10 is manufactured.

In some cases, in the exposed end portion of the inner pipe 12, there isformed a seal groove for mounting an O ring. In this case, as describedbefore, since the thickness of the exposed end portion of the inner pipe12 is uniform, such seal groove can be formed by punching or by rollingwithout giving rise to a crack therein. And, the dimensional precisionof the seal groove can be maintained with ease. Also, in some cases, theend portion of the inner pipe 12 is brazed. In this case, since thethickness of the inner pipe end portion is uniform and the hole of theinner pipe 12 provides sufficient roundness, poor brazing is hard tooccur.

Further, because at least the outer pipe 11 is uncut and is left as itis, the cutting margin of the duplex pipe 10 can be minimized to therebyreduce the quantities of cut powders produced, the cleaning control ofthe cut powders can be facilitated, and poor sealing possibly caused bycontamination can be prevented positively.

Second Embodiment

FIGS. 5A to 5D are respectively conceptual views of a duplex pipe endworking method according to a second embodiment of the invention as wellas a working procedure to be executed by a duplex pipe end workingapparatus which can enforce the present duplex pipe end working method.

The second embodiment is different from the first embodiment, in whichthe slit forming step is enforced after completion of the rib cuttingstep, in that a rib cutting step is enforced after completion of a slitforming step.

In the second embodiment, firstly, as shown in FIG. 5A, an outer pipe 11is chucked by a clamp 20 to thereby hold a duplex pipe 10, and theduplex pipe 10 is slitted; that is, at and from the end face of theduplex pipe 10 up to the portion of the duplex pipe 10 that correspondsto the exposed length of the inner pipe 12, there is formed a slit 21 inthe duplex pipe 10, specifically, in the outer pipe 12 and connectingribs 13 (slit forming step).

In the slit forming operation, similarly to the first embodiment, thereis used a metal saw 22. While rotating the duplex pipe 10 and metal saw22, the metal saw 22 is moved forward in the direction of an arrow markshown in FIG. 5A to thereby form a slit 21. The width of the slit 21 isof the order of 1 mm. The slit 21 is formed on until it reaches theouter peripheral surface of the inner pipe 12. However, while taking itinto consideration that the center of the inner pipe 12 is slightlydisplaced from the center of the outer pipe 11, preferably, the slit 21may be formed in such a manner that the connecting ribs 13 can berespectively left in part by a slight dimension (for example, of theorder of 0.1 mm).

Next, as shown in FIGS. 5B and 5C, the connecting ribs 13 arerespectively cut along the axial direction of the duplex pipe 10starting at and from the end face of the duplex pipe 10, that is, a ribcutting operation is executed (rib cutting step). In the rib cuttingoperation, from the viewpoint of reduction in the cutting margins of theconnecting ribs 13, preferably, only the base end portions of theconnecting ribs 13, that is, only the portions of the connecting ribs 13that are connected to the outer peripheral surface 12 a of the innerpipe 12 may be cut.

In the rib cutting operation, similarly to the first embodiment, thereis used a cutting tool 30. In operation, while rotating the duplex pipe10 and cutting tool 30, the cutting tool 30 is moved along the axialdirection of the duplex pipe 10 to thereby cut the connecting ribs 13.Such cutting of the connecting ribs 13 is executed on until the leadingend of the cutting tool 30 reaches the slit 21. By the way, in the ribcutting operation, alternatively, the duplex pipe 10 may not be rotated.

With such cutting of the connecting ribs 13, on the leading end side (inFIG. 5C, on the right side) of the duplex pipe 10 that is locatedforwardly of the slit 21, the connection between the outer and innerpipes 11 and 12 is cut. Therefore, as shown in FIG. 5D, in case wherethe leading end side portion of the duplex pipe 10 located forwardly ofthe slit 21 is pulled out, the inner pipe 12 is projected outwardly ofthe outer pipe 11 and is thereby exposed to the outside. This completesthe duplex pipe end working operation.

The cutting tool 30 used in the second embodiment is the same as shownin the first embodiment and thus the description thereof is omittedhere.

In operation, the cutting tool 30 is moved forward toward the duplexpipe 10 with the axis thereof coincident with the axis of the outer pipe11. The end portion 10 a of the duplex pipe 10, in which the slit 21 isformed, is connected only by the inner pipe 12 and, therefore, the endportion 10 a is flexible to a certain degree. Thus, even in case wherethe center of the inner pipe 12 is slightly displaced from the center ofthe outer pipe 11, the guide pin 33 can be inserted into the inner pipe12 smoothly, so that the above-mentioned displacement of the inner pipe12 can be corrected. Also, the smooth insertion of the guide pin 33 canprevent the axis of the cutting tool 30 from swinging or oscillating.

In case where the cutting tool 30 is moved further forward after theguide pin 33 is inserted into the inner pipe 12, the inner pipe 12 isinserted into the guide hole 31, while the outer peripheral surface 12 athereof is being guided by the inner peripheral surface of the of theguide hole 31. Such insertion of the inner pipe 12 into the guide hole31 can also correct the above-mentioned displacement of the inner pipe12.

According to the second embodiment, in addition to various operationeffects which have been already discussed in the first embodiment, therecan be further obtained the following operation effects in lining withthe fact that the slit forming operation is executed before the ribcutting operation.

That is, in the first embodiment, the end portion 10 a of the duplexpipe 10 in the rib cutting operation remains connected by the outer pipe11, connecting ribs 13 and inner pipe 12; but, on the other hand, in thesecond embodiment, the end portion 10 a of the duplex pipe 10 in the ribcutting operation is connected only the inner pipe 12. Therefore,according to the working procedure of the second embodiment, whencompared with the working procedure of the first embodiment, theflexibility of the end portion 10 a is increased, which can furtherfacilitate the insertion of the guide pin 33 into the inner pipe 12.Accordingly, the displacement of the inner pipe 12 can be corrected moreeasily as well as the centering of the inner pipe 12 can be attainedmore easily.

Also, in the rib cutting operation, the forward moving position of thecutting tool 30 can be visually confirmed through the slit 21. This canprevent the cutting tool 30 from cutting the connecting ribs 13excessively in the axial direction of the duplex pipe 10.

Further, since the slit forming operation is carried out before the ribcutting operation, in the slit forming operation, in the respectiveconnecting ribs 13, there are not present any cut surface extendingalong the axial direction thereof, which can eliminate a fear that theouter peripheral surface of the inner pipe 12 can be damaged by such cutsurface.

Third Embodiment

Now, FIGS. 6A and 6B respectively show the concept of a third embodimentaccording to the invention; that is, they are conceptual views of aworking procedure for cutting connecting ribs 13 according to the thirdembodiment of the invention.

The third embodiment is similar to the second embodiment in that a ribcutting step is carried out after a slit forming step but the thirdembodiment is different from the second embodiment in the rib cuttingmethod and cutting tool.

A cutting tool 40 employed in the third embodiment, similarly to thepreviously described cutting tool 30, comprises a guide hole 41 intowhich an inner pipe 12 can be inserted while guiding the outerperipheral surface 12 a of the inner pipe 12, a cutting device 42 forcutting connecting ribs 13, and a guide pin 43 which is disposed in theguide hole 41 and also can be inserted into the inner pipe 12 whileguiding the inner peripheral surface 12 b of the inner pipe 12.

However, the cutting tool 40 is disposed in such a manner that it can bepressed in the axial direction thereof; that is, in operation, accordingto a punch method, the cutting tool 40 is pressed in the axial directionof the duplex pipe to thereby cut the connecting ribs 13. In thisrespect, the present embodiment is different from the previouslydescribed working method and cutting tool 30 in which the connectingribs 13 are cut according to a rotating method. In the presentembodiment, due to use of the punch method, there is eliminated theopening 34 that is formed in the cutting tool 30, so that the cuttingdevice 42 is formed such that it extends in a solid state over theentire periphery of the cutting tool 40.

By the way, although there is omitted the detailed description thereof,in the cutting tool 40 of a punch type, according to a similar conceptto the cutting tool 30 of a rotation type, the shape of the cuttingdevice 42 is set so as to be able to enhance the surface precision ofthe inner pipe outer peripheral surface 12 a as well as the relief shapethereof is set so as to be able to reduce the working resistance.

Also, in the case of a clamp 45 which is used in the rib cutting step,it is capable of chucking even the portion of the outer pipe 11 locatedon the leading end side thereof beyond the slit 21, and there is furtherdisposed a projecting ring 46 which can be inserted into the slit 21.The reason for this is that, when the cutting tool 40 is pressed, theinner pipe 12 can be prevented from buckling. By the way, the dimensionfor chucking the leading end side portion of the outer pipe 11 beyondthe slit 21 is set in the range not interfering with the displacementcorrecting function with which the guide pin 43 can be inserted into theinner pipe 12 to thereby correct the displacement of the inner pipe 12.

Even in the case of the cutting tool 40 of a punch type, in order to beable to cut the connecting ribs 13 after correction of the displacementof the inner pipe 12, the thickness of the inner pipe 12 can be setuniform over the entire periphery thereof. Further, when compared withthe cutting tool 30 of a rotation type, the quantities of cut powdersgenerated can be reduced remarkably and thus the cleaning control of thecut powders can be facilitated further.

By the way, in the working procedure in which, as in the firstembodiment, the slit forming step is carried out after completion of therib cutting step, instead of the cutting tool 30 of a rotation type,there can also be used the cutting tool 40 of a punch type.

Fourth Embodiment

Now, FIG. 7 is a perspective view of a cutting tool 60 which is employedin a fourth embodiment according to the invention.

The cutting tool 60 employed in the fourth embodiment, similarly to thepreviously described cutting tools 30 and 40, comprises a guide hole 61into which an inner pipe 12 can be inserted while guiding the outerperipheral surface 12 a of the inner pipe 12, a cutting device 62 forcutting connecting ribs 13, and a guide pin 63 which is disposed in theguide hole 61 and also can be inserted into the inner pipe 12 whileguiding the inner peripheral surface 12 b of the inner pipe 12.

However, the present cutting tool 60 is different from the previouslydescribed cutting tools 30 and 40 in that the cutting device thereof canbe replaced. The cutting tool 60 includes a cylindrical-shaped holder 66in which there is formed a guide hole 61. The leading end portion of theholder 66 is cut away at three positions thereof, whereby there areformed three openings 67 each communicating with the guide hole 61, andthree cutting device support portions 68. To one end portion of each ofthe cutting device support portions 68, there is replaceably fastenedthe cutting device 62 by a bolt 69. The guide pin 63 is connected to theholder 66 and can be rotated together with the holder 66.

By the way, although there is omitted the detailed description thereof,in the cutting tool 60 as well, according to a similar concept to thecutting tool 30, the shape of the cutting device 62 is set so as to beable to enhance the surface precision of the inner pipe outer peripheralsurface 12 a as well as the relief shape thereof is set so as to be ableto reduce the working resistance.

According to the thus structured cutting tool 60, in case where thecutting device 62 is worn as it cuts the connecting ribs 13, it can bereplaced with a new cutting device 62, which makes it possible to usethe holder 66 repeatedly; that is, the holder 66 can be used moreeffectively.

By the way, in the case of the cutting tool 40 of a punch type as in thethird embodiment as well, it can be modified in such a manner that thecutting device 42 can be freely replaced with respect to the sameholder.

Fifth Embodiment

Now, FIGS. 8A and 8B respectively show the concept of a fifth embodimentaccording to the invention; that is, they are conceptual views of aworking procedure for forming a slit 21 according to the fifthembodiment of the invention.

The slit forming operation may also be executed using not only thepreviously described metal saw 22 but also such a spin cutter 50 asshown in FIGS. 8A and 8B. Here, in FIGS. 8A and 8B, reference character51 designates a rotatable receiving roller which can be contacted withthe outer peripheral surface 11 a of the outer pipe 11.

In the case of a slit forming operation using the spin cutter 50, whencompared with the slit forming operation using the metal saw 22, thequantities of cut powders generated can be reduced remarkably, which inturn can further facilitate the cleaning control of the cut powders.

Other Modifications

In the above-mentioned embodiments of the invention, there have beenillustrated the cutting tools 30, 40 and 60 in which the guide pins 33,43 and 63 are respectively disposed in their associated guide holes 31,41 and 61; however, the invention is not limited to them. For example,since the inner pipe 12 is inserted while guiding the inner pipe outerperipheral surface 12 a by its associated one of the guide holes 31, 41and 61 of the cutting tools 30, 40 and 60, even in case where the guidepins 33, 43 and 63 are omitted, the displacement of the inner pipe 12can be corrected only by its associated one of the guide holes 31, 41and 61. Omission of the guide pins 33, 43 and 63 is especially effectivewhen the center of the inner pipe 12 is displaced from the center of theouter pipe 11 but variations in the thickness of the inner pipe 12 arewithin the allowable range.

Application Example to Joint

Now, FIG. 9 is a section view of a joint 60 for connecting together twoduplex pipes the end portions of which have been worked according to theinvention.

In FIG. 9, first and second duplex pipes 100 and 200 are respectivelypipes which are used as refrigerant pipes in a cooling cycle of an airconditioner for a car, and also which respectively include outer andinner pipes 101, 102 and 201, 202; and, a low-pressure-gas refrigerantis allowed to flow through the outer pipes 101 and 201, whereas ahigh-pressure-gas refrigerant is allowed to flow through the inner pipes102 and 202. The end portions of the first and second duplex pipes 100and 200 are respectively worked according to the invention, while theinner pipes 102 and 202 are respectively projected by a given lengthoutwardly of the outer pipes 101 and 201 and are thereby exposed to theoutside.

The joint 60, which is a joint of a flange type, is structured in thefollowing manner: that is, a first outer pipe seal member 110 is brazedto the outer pipe end portion 101 a of the first duplex pipe 100; and, asecond outer pipe seal member 210 is brazed to the outer pipe endportion 201 a of the second duplex pipe 200. Between the first andsecond outer pipe seal members 110 and 210, there is interposed an Oring 301, thereby being able to prevent the leakage of thelow-pressure-gas refrigerant flowing through the outer pipes 101 and201.

In the inner pipe end portion 102 a of the first duplex pipe 100, thereis formed a first inner pipe seal portion 120 and, in the inner pipe endportion 202 a of the second duplex pipe 200, there is formed a secondinner pipe seal portion 220. Between the first and second inner pipeseal portions 120 and 220, there is interposed an O ring 401, whichmakes it possible to prevent the leakage of the high-pressure-gasrefrigerant flowing through the inner pipes 102 and 202.

The first inner pipe seal portion 120 includes a flare portion 121 whichis spread. The flare portion 121 can be formed by punching the innerpipe end portion 102 a into a flare shape. On the other hand, in thesecond inner pipe seal portion 220, there is formed a ring groove 221into which the O ring 401 can be mounted. The ring groove 221 can beformed by punching or rolling the inner pipe end portion 202 a. Thesecond inner pipe seal portion 220 can be fitted into the flare portion121 of the first inner pipe seal portion 120.

The inner pipe end portions 102 a and 202 a, which have been workedaccording to the invention, are uniform in thickness. Therefore, even incase where a punching operation or a rolling operation is enforced onsuch inner pipe end portions 102 a and 202 a, there is no fear thatthere can occur cracks in them, and thus the flare portion 121 and ringgroove 221 can be formed. Also, the dimensional precision of the flareportion 121 and ring groove 221 can also be maintained easily.

And, a through bolt 501 is inserted through the two outer pipe sealmembers 110 and 210 and a nut 502 is fastened to the through bolt 501,whereby the two duplex pipes 100 and 200 can be connected together.

As has been described heretofore, according to the first to fifthaspects of the invention, there is provided a duplex pipe end workingmethod which can be suitably applied to an operation to skin or cut theend portion of a duplex pipe comprising an outer pipe, an inner pipe andconnecting ribs molded into an integral body by extrusion working or bydrawing working. That is, with use of the present duplex pipe endworking method, the thickness of the inner pipe can be made uniform,burrs can be prevented from occurring in the end portions of theconnecting ribs, and production of cut powders can be reduced.

Especially, according to the second aspect of the invention, in additionto the above effects, in linking with the enforcement of the slitforming operation before the rib cutting operation, the end portion ofthe inner pipe is increased in flexibility, which makes it possible tocorrect the displacement of the inner pipe easily as well as tofacilitate the centering of the inner pipe. Also, the advancing positionof the cutting tool can be visually confirmed through the slit, therebybeing able to prevent the cutting tool from cutting the connecting ribsexcessively in the axial direction of the duplex pipe. Further, in theslit forming operation, in the connecting ribs, there exists no cutsurface extending along the axial direction of the duplex pipe. Thiseliminates a fear that the inner pipe outer peripheral surface can bedamaged by such cut surface.

Also, according to the fifth aspect of the invention, the thickness ofthe inner pipe can be restricted according to the clearance dimensionbetween the cutting device and guide pin. Thanks to this, in case wherethe inner pipe is swaged, or even in case where the inner pipe is foundto vary in thickness at the stage when the duplex pipe is manufactured,the thickness of the inner pipe can be made uniform.

And, according to a duplex pipe end working apparatus as set forth inthe sixth to tenth aspects of the invention, in the operation to skin orcut the end portion of a duplex pipe comprising an outer pipe, an innerpipe and connecting ribs molded into an integral body by extrusionworking or by drawing working, the thickness of the inner pipe can bemade uniform, burrs can be prevented from occurring in the end portionsof the connecting ribs, and production of cut powders can be reduced.

Especially, according to the ninth aspect of the invention, a cuttingdevice, which is worn as it cuts the connecting ribs, can be replacedwith a new cutting device; and, according to the tenth aspect of theinvention, the thickness of the inner pipe can be restricted accordingto the clearance dimension between the cutting device and guide pin.Thanks to this, in case where the inner pipe is swaged, or in case wherethe inner pipe is found to vary in thickness at the stage when theduplex pipe is manufactured, the thickness of the inner pipe can be madeuniform.

1. A method for working an end portion of a duplex pipe including anouter pipe, an inner pipe disposed inside the outer pipe, and aplurality of connecting ribs respectively for connecting the outer pipeand the inner pipe to cut the outer pipe and the connecting ribs toproject and expose the inner pipe from the outer pipe, the methodcomprising: chucking the duplex pipe; cutting the outer pipe and theconnecting ribs at a predetermined position to form a slit in the outerpipe and the connection ribs; then cutting the connecting ribs from theend portion along an axial direction of the duplex pipe; and removingthe outer pipe and the connecting ribs which have been cut to expose apart of the inner pipe.
 2. The method as claimed in claim 1, wherein acutting tool including a guide hole for guiding the outer peripheralsurface of the inner pipe and for allowing the inner pipe to be insertedthereinto, and a cutting device for cutting the connecting ribs are usedfor cutting the connecting ribs.
 3. The method as set forth in claim 2,wherein, while rotating the cutting tool, the cutting tool is moved inthe axial direction to cut the connecting ribs.
 4. The method as claimedin claim 2, wherein the cutting tool is pressed from the end portion ofthe duplex pipe in the axial direction to cut the connecting ribs. 5.The method as claimed in claim 2, wherein a guide pin is disposed in theguide hole, and allowed to be inserted into the inner pipe while guidingthe inner peripheral surface of the inner pipe.